The present invention relates to a polymeric compound suitably used in an electronic device applicable to functional devices including a luminescent device, such as an organic electroluminescent (EL) device or a light-emitting diode (LED), and an organic semiconductor device. The present invention also relates to a process for producing the polymeric compound and an electronic device using the polymeric compound.
In recent years, extensive studies on organic compounds for use in functional devices such as a luminescent device and a semiconductor device have been conducted. A typical example thereof include one regarding a photoconductive member used in electrophotography. The photoconductive member has been widely used in copying machines, electrophotographic printers, etc., in view of its advantages, such as excellent productivity and good functional properties.
Further, research and development regarding organic materials for use in a luminescent device, particularly an EL device, has been conducted extensively in recent years.
More specifically, C. W. Tang et al. have proposed an organic EL device having a function-separation type layer structure including a carrier transport layer and a luminescence layer (e.g., Appl. Phys. Lett., vol. 51, pp. 913 (1987) and U.S. Pat. No. 4,769,292).
In the circumstances, liquid crystal materials have been applied to the above-mentioned functional devices. More specifically, a high performance device has been prepared by utilizing a higher order (molecular alignment) structure of liquid crystal. For example, according to a study by Hanna on liquid crystalline organic semiconductors, Ohyou Butsuri, Appl. Phys., vol. 68, no. 1, pp. 26-32 (1999), it has been confirmed that a smectic liquid crystal showed a high carrier transport performance. With respect to the carrier transport performance, particularly electron and hole transport performances, a smectic liquid crystal having a (molecular alignment) structure of higher order represented by a hexagonal system order exhibits an especially higher carrier transport performance in its higher order liquid crystal phase of smectic B (SmB) or smectic E (SmE) than in its lower order liquid crystal phase of smectic A (SmA) or smectic C (SmC) in which the smectic liquid crystal only has a liquid like order.
However, it is difficult to stably realize the higher order smectic phase (e.g., SmB or SmE) wherein a smectic liquid crystal has the higher order structure described above in a broader temperature range. Further, a highly reliable electronic device utilizing such a higher order smectic phase has not been readily provided.
An object of the present invention is to provide a polymeric compound having a higher order smectic phase capable of practical use.
Another object of the present invention is to provide a process for producing the polymeric compound.
A further object of the present invention is to provide an electronic device using the polymeric compound with high reliability, thus improving device characteristics when used as a functional device, such as a luminescent device or an organic semiconductor device.
According to the present invention, there is provided a polymeric compound having a smectic phase 25 and a hexagonal (crystal) system order in the smectic phase.
According to the present invention, there is also provided a process for producing a polymeric compound comprising the steps of polymerizing a liquid crystal compound having a polymerizable functional group in a state wherein the liquid crystal compound has a hexagonal system order.
The present invention provides an electronic device comprising at least one substrate, two electrodes disposed on said at least one substrate, and a polymer layer of at least one species of polymeric compound disposed between the two electrodes, wherein said at least one species of polymeric compound has a smectic phase and a hexagonal system order in the smectic phase.
As a result of our study, it has been found that a polymeric compound (solidified layer) having a hexagonal system order exhibits excellent functional properties in a higher order liquid crystal phase and that it becomes possible to realize a highly reliable electronic device excellent in environmental stability by using the polymeric compound.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.